diff --git a/doc/retrace.md b/doc/retrace.md
index ea6a151..ae22ff1 100644
--- a/doc/retrace.md
+++ b/doc/retrace.md
@@ -209,7 +209,7 @@
 should carry the reported position to the next frame and use the
 `outlineCallsite` to obtain the correct position.
 
-### Outline Call Site (Introduced at version 2.0)
+### Outline Call Site (Introduced at version 2.0, updated at 2.2)
 
 A position in an outline can correspond to multiple different positions
 depending on the context. The information can be stored in the mapping file with
@@ -221,10 +221,14 @@
         'outline_pos_1': callsite_pos_1,
         'outline_pos_2': callsite_pos_2,
          ...
-     }
+     },
+     'outline': 'outline':'La;a()I'
   }
 ```
 
+The `outline` key was added in 2.2 and should be the residual descriptor of the
+outline.
+
 The retracer should when seeing the `outline` information carry the line number
 to the next frame. The position should be rewritten by using the positions map
 before using the resulting position for further retracing. Here is an example:
@@ -240,7 +244,8 @@
   5:5:int outlineCaller(int):100:100 -> s
   27:27:int outlineCaller(int):0:0 -> s
 # { 'id':'com.android.tools.r8.outlineCallsite',
-    'positions': { '1': 4, '2': 5 } }
+    'positions': { '1': 4, '2': 5 },
+    'outline':'La;a()I'}
 ```
 
 Retracing the following stack trace lines:
@@ -273,4 +278,30 @@
 ```
 
 It does not matter if the mapping is an inline frame. Catch all ranges should
-never be used for overloads.
\ No newline at end of file
+never be used for overloads.
+
+### Residual signature (Introduced at 2.2)
+
+The residual signature information was added to mitigate the problem with no
+right hand side signature in mapping files. The information should be placed
+directly under the first occurrence of a field or method.
+
+```
+com.bar -> a:
+com.foo -> b:
+  com.bar m1(int) -> m2,
+  # { id: 'com.android.tools.r8.residualsignature', signature:'(Z)a' }
+```
+
+Similar for fields:
+```
+com.bar -> a:
+com.foo -> b:
+  com.bar f1 -> f2,
+  # { id: 'com.android.tools.r8.residualsignature', signature:'a' }
+```
+
+If the residual definition has changed arguments or return type then the
+signature should be emitted. The residual signature has no effect on retracing
+stack traces but they are necessary when interacting with residual signatures
+through the Retrace Api or for composing mapping files.
\ No newline at end of file